1. Field of the Invention
The present invention is directed to a method of and apparatus for forming a coating having at least one fade zone on a surface of an article and, more particularly, to a method of and apparatus for pyrolytically depositing one or more metal oxide coatings having at least one fade zone on a portion of a moving float ribbon of glass. The present invention is also directed to articles having a coating formed over a surface of the article, which coating includes at least one fade zone, particularly articles made from the above-described coated float glass ribbon.
2. Description of the Prior Art
As used herein, the term "fade zone" refers to an area or zone of a coated article, e.g. a coated substrate, having a first limit spaced apart from a second limit, in which a coating present over the substrate within the zone gradually decreases in thickness, intensity and/or density from a first thickness, intensity and/or density at the first limit to a second lesser thickness, intensity and/or density at the second limit. The term also refers to an area or zone in which a coating present over the substrate gradually decreases in thickness, intensity and/or density from a first thickness, intensity and/or density at a first limit to an absence of coating over the substrate at a second limit. Such coatings may also be referred to as "graded" or "gradient" coatings.
It is known to form a coating having a fade zone over a substrate. For example, U.S. Pat. No. 3,004,875 to Lytle discloses applying a band of metal salt composition at an oblique angle toward an edge portion of a substrate to be coated, using a shield to limit the area of application of the coating composition. The resulting band is of gradually increasing intensity from its boundary portion adjacent to the edge of the shield because of eddies that evolve beneath the shield near the edge of the shield during the coating operation.
Also, for example, U.S. Pat. No. 2,676,114 to Barkley discloses various methods of producing graded coatings by vacuum deposition using mechanical barriers to apply graded coatings to glass sheets.
U.S. Pat. No. 3,305,336 to Browne et al. discloses a spray gun system used in conventional spray techniques as opposed to electrostatic spray techniques, for applying a film on a glass surface. The film is formed as a band having a major area of maximum intensity bordered by a fade-out line that defines a fade-out area in which the transmittance of the film gradually and progressively increases until its value reaches the clarity of the glass substrate.
U.S. Pat. No. 4,138,284 to Postupack and U.S. Pat. No. 4,208,446 to Postupack et al., disclose a method of forming a graded shade band on a substrate by electrostatically spraying a dye composition past a grounded electroconductive shield or multiple grounded shield system toward a substrate to control the location of the cut-off line between the coated and uncoated regions of the substrate and to limit the amount of dye deposited in the vicinity of the cut-off line to form a graded coating.
Forming coatings, particularly metal oxide coatings, by spray pyrolysis is also known. For example, U.S. Pat. Nos. 3,660,061; 4,719,126 and 4,719,127, each of which are hereby incorporated herein by reference, describe the pyrolytic deposition of metal oxide films onto glass surfaces.
A relatively complex apparatus for forming coatings by spray pyrolysis is described in U.S. Pat. No. 4,111,150, which is hereby incorporated herein by reference. The apparatus is described as being able to obtain special effects in coatings, such as graded or varied thickness films by arranging sets of coating composition dispensers which are moved by a continuous traveling chain over a conveyor to coat glass traveling on the conveyor.
It would be advantageous to provide methods of and apparatus for forming pyrolytically deposited films or coatings having a fade zone, which methods and apparatus are in addition to those that are presently available and, more particularly, which do not require complex apparatus to obtain such a coating.